朱溪超大型钨铜矿床流体演化与成矿机制: 来自流体包裹体, 同位素和矿物原位微区地球化学的约束

Zhuxi W-Cu deposit is a recently found world-class skarn type deposit. Previous studies have shown that this deposit belongs to reduced skarn type. However, the metallogenic mechanism and fluid evolution process of this deposit are still not well known. The reduced skarn W-Cu deposits are very important deposit type which commonly form large and super large deposit in the world in contrast to the oxidized skarn deposits. Most research works on the reduced skarn type W-Cu deposits were conducted around 1980-1990s and the ore genetic models are still in dispute. This project will take Zhuxi deposit as a case study for the reduced skarn type W-Cu deposit, to investigate the ore deposit geology, mineral paragenetic stages, and hydrothermal evolution history, to measure the composition, salinity and temperatures of the fluid inclusions, as well as the in-situ analysis of trace element compositions of scheelite and apapite, and Sr isotopic compositions of apatite, S isotopic compositions of pyrite and chalcopyrite, as well as Pb and H-O isotope analysis. Based on these data, the hydrothermal fluid composition, pH, oxygen fugacity, Cl and F composition, and the source of fluids and ore-forming materials will be discussed. The goal of this project is to build a metallogenic mechanism for the Zhuxi W-Cu deposit and the results will improve our understanding of the reduced skarn W-Cu deposit.

江西朱溪钨铜矿床是近年来新发现的一个超大型矽卡岩矿床, 前人研究初步确定这是一个还原型矽卡岩钨铜矿床。但对该矿床成矿流体演化过程和成矿机制的研究仍较薄弱。不同于氧化型矿床，还原型矽卡岩矿床往往形成大型超大型矿床，但国内外对该类型矿床成矿作用研究较少，对于此类超大型矽卡岩型钨铜矿床的许多研究集中于上世纪80-90年代，且成矿模式存在争议。本项目拟以朱溪矿床为研究对象，结合野外和室内镜下观察，划分成矿期次，对不同期次的流体包裹体开展成分分析和显微测温。测定矿床H-O和Pb同位素成分，同时开展矿物原位微区分析以获得白钨矿的微量元素，磷灰石微量元素和Sr同位素组成，黄铁矿和黄铜矿的原位硫同位素组成。综合上述工作，探讨朱溪钨铜矿床流体演化过程中流体成分，氧逸度，pH值，卤素等物理化学条件变化过程，以及成矿流体和成矿物质来源, 建立朱溪钨铜矿床的成矿模型，丰富还原型矽卡岩W-Cu矿床的成矿理论体系。

此项目对朱溪W-Cu矽卡岩矿床开展了系统的地质特征描述和地球化学分析。此研究划分了矿化期次；采用了高精度岩浆和热液的锆石、磷灰石U-Pb定年；深部富W矿体和地表富Cu矿体中的硫化物S同位素分析；矽卡岩矿物和矿石矿物白钨矿显微结构和原位成分分析以及相应的包裹体研究；还系统分析了朱溪花岗岩的全岩地球化学和Sr-Nd同位素组成。确定了朱溪最晚期的花岗斑岩与矿化的成因联系；确定了包裹体主要为H2O–NaCl/KCl/CaCl2±CH4/C2H4体系。成矿温度从500℃到150℃不断降低；早期以岩浆水为主，后期有大气水的混合。